The height of a right circular cone is decreased by 6 percent. Find the percentage that the radius of the base must be decreased by so that the volume decreases by 20 percent. Recall that the formula for the volume of a right circular cone is

Question

V =
πr2h 3

Answer 1

V=1/3 PI r^2 h
V'=1/2 PI r'^2 h'

v'=.8v, h'=.94h

v'/v=.8= (r'/r)^2 *.94

r'/r= sqrt(.8/.94)=.92
so r must be reduced 8 percent